Antenna system



3 Sheets-Sheet 1 G. L. MYDLIL ANTENNA SYSTEM July 2, 1940.

Filed Dec. 7. 1938 July 2, 1940. cs. 1.. MYYDLIL 2,206,820

ANTENNA SYSTEM Filed Dec. 7, 1938 3 Sheets-Sheet 2 5%2ae @245 Z @J/ZZ July 2, 1940. MYDLlL 2,206,820

ANTENNA SYS TEM Filed Dec. 7, 1938 3 Sheets-Sheet} ANTENNA VOLTAGE GAIN COLLECTOR WITHOUT BOOSTER FREQUENCY m NOISE WITHOUT BOOST R NOISE TO SIGNAL NOISE WITH BOOSTER I $206122??? 62/51: @J/ZZ/ SENSITIVITY Q 14m MICROVOLTS m Patented July 2, 1940 Gus L- Mydlll, Chico;

u 88 8110! to Galvin Manufacturing Corporation, Chicago, 11]., a

corporation of Illinois Application December 1, 1938, Serial No. 244,468 15 Claims. (crest-3s) My invention relates in general to antenna systems for radio apparatus, and more in particular to an antenna system for a radio receiver to increase the normal signal energy input to such a receiver from such antenna system.

One of the important problems to overcome in radio antenna design is the matter of space inv which an antenna system and particularly the signal collector or aerial of such system is to be mounted. Lack of space in by far the greater majority of radio installations requires that the aerial be smaller than the most desirable length to conform with the lengths of radio waves being received. This is particularly true with reference to wave lengths in the broadcast spectrum. Each reduction in length of the aerial below the normal relation to the length-of the radio waves being received reduces the signal energy abstracted from a passing radio wave. In many instances, although considerable space may be available for mounting an aerial, it is either inconvenient or too costly to install a long serial, or because of wind resistance against the aerial, or disflguration in general appearance, it is extremely undesirable and sometimes impossible to have a long aerial. In an short to make up for lack of aerial length and hence low signal energy, it has been necessary to design the radio receiver tube circuit so as to increase the gain, sensitivity and amplification in the tube circuit. As the amplification is increased in the tube circuit there is an increase in the thermal agitation in the tubes which raises the noise level in the receiver circuit and lowers the signal to noise ratio which in turn affects the quality of reproduction from the radio receiver.

Aside from the design of the tube circuit itself in the radio receiver, the prior art has attempted to correct these diiilculties by providing variable couplings at the input stage in the receiver be tween the antenna system as represented by a signal collector or aerial and lead-in, and the receiver circuit. An inductance'has been inserted into the receiver circuit in the input stage as well as in other positions in such circuit to increase the amount of signal energy introduced into the radio receiver by an antenna system comprising an aerial and lead-in. These, and other eiforts with which I am familiar have either been totally ineffective so far as increasing signal energy is concerned or they have increased the signal energy only so slightly that the improvement did not warrant the cost of the installation. This is particularly true with reference to installations of radio receivers on mobile craft, for reception over the broadcast spectrum. Considering only the efl'ort to raise the signal to noise ratio and increase the signal energy by the tube circuit design, these efforts have increased the cost of such circuits and in many instances affected the quality of the radio reproduction. None 01 the prior art efforts so far as I know, have been effective enough to make possible the use of short aerials for signal collectors in the nature of one foot to two feet, for instance, and still retain an economical receiver circuit design and high quality reproduction.

An object of my invention is to provide an improved antenna system which will materially increase radio signal energy in the antenna system itself, and make possible the use of a relatively short aerial or signal collector in such antenna, system.

A further object of my invention is to provide sturdy, simple, and relatively inexpensive apparatus in my antenna system which will materially increase the signal strength over a particular section of a complete broadcast signal range, or which will effect such increase in signal strength to a material degree over an entire range of broadcast frequencies.

A still further object of my invention is to provide an antenna system for increasing the signal energy in the antenna system itself which can. be adapted with equal ease as an accessory installation on radio receiver equipment, or as original equipment.

One of the features of my invention is the provision of an antenna system with a signal collector so short that it is readily mounted and then inconspicuous on all types of mobile craft, such as automobiles, airplanes, ships, and the like, and in this shorter length in a signal collector, still provides signal energy greately in excess of that introduced into a radio receiver from a longer, more expensive, more conspicuous, and less desirable signal collector of the prior art.

Another feature of my invention is the provision of an antenna system in which the signal energy can be increased to a point, even with a short signal collector, that the radio receiver circult to which it is applied can be simplified and operated at a lower amplification level to reduce the noise generated in the receiver circuit itself, and yet provide high volume, high quality repro duction. In this connection, even though the same noise level is maintained in the radio receiver, the signal to noise ratio will always be higher and more favorable due to the increased signal energy introduced into the radio receiver circuit.

Other objects and features of my invention will be apparent from the following description taken with the drawings, in which:

Fig. 1 is a perspective view oi. one embodiment.

Fig. 2 is an enlarged vertical sectional view oi the signal collector and variable inductance portion of the structure illustrated in Fig. 1.

Fig. 3 is a diagrammatic illustration of the antenna system of Fig. 1 connected to a representative radio receiver.

Fig. 4 is an illustration partially in section and partially in elevation of a modified embodiment of my invention.

Fig. 5 is an enlarged detail view of the junction box from the structure of Fig. 4.

Fig. 6 is an illustration similar to Figs. 1 and 4 of a still further modification of my invention, utilizing, however, the junction box of Figs. 4 and 5. i

Fig. 7 graphically shows the antenna voltage gain in embodiments of my invention utilizing signal collectors of various lengths, in comparison with an antenna system employing a much longer signal collector and a shielded lead-in directly intermediate the. signal collector and a radio receiver.

Fig. 8 shows graphically the signal to noise ratio in a receiver system with my antenna system, in comparison with an antenna system using simply an aerial or signal collector and shielded lead-in.

In practicing my invention, I provide an antenna system for connecting to a radio receiver, which system includes an aerial or signal collector and an inductance in series with said signal collector and in direct or substantially direct connection therewith, and a shielded lead-in connected at the opposite end of the inductance. The connection between the aerial and inductance is accomplished with the introduction of a very minimum of impedance. The inductance may be maintained at a fixed inductance value for resonating the signal collector so as to match the signal frequency therein with the frequencies to which the radio receiver is tuned. Such an inductance is most effective to increase the signal voltage in the antenna system primarily for a particular group of frequencies out of the entire frequency range of the radio receiver, and is normally less effective over the remaining frequencies in such frequency range. The inductance value of the inductance coil in my system may also be varied to tune the antenna system to correspond with the tuning of the radio receiver at each frequency and thus increase the voltage in the antenna system materially over the entire frequency range of the receiver. The inductance of such coil can be varied by moving an iron slug therein. The iron slug may be mechanically linked with the tuning systems of the radio receiver to which my antenna system is applied so that the slug is moved in accordance with the movement-of such tuning system, or such slugs can be adjusted independently of a tuning movement of a radio receiver to which the antenna system is applied by first tuning such-receiver and then positioning the slug in the inductance through a remote drive at a point where the speaker output for the particular tuning of the receiver is maximum.

Referring now to Fig. 1, a complete apparatus embodying my invention is illustrated, and includes an aerial or signal collector [0 provided in a suitable metal wire or rod rigidly supported in a closed junction box llhousing a variable inductance coil, as will be explained, which in turn is connected with a shielded lead-in conductor l2 for connection to the input circuit of a radio receiver. The inductance of the coil is varied by means including a flexible shaft l3 extending out of the junction box for operative connection with a radio receiver l4. A bendable drive wire I6 is carried in the usual covering I'I of the flexible shaft l3, and such covering is removably mounted at l8 onto the outer housing IQ for the radio receiver I4. The drive wire I6 is moved linearly upon rotation of the tuning condenser 2l as a result of a connection to the shaft 22 of the variable condenser through a cam 23 fixedly secured thereon and having a cam slot 24 adjacent one edge for carrying therein and moving therewith a hooked link 26. The link 26 has a hook or projection 2'! on the end thereof riding directly in the slot 24 and is connected at the other end through a coupling 28, which is desirably provided in insulating material, and is suitably secured to the drive wire I6 as shown in Fig. 1. Although a metal coupling maybe employed at 28, it is preferred to use an insulating member so as to prevent the introduction of interference noises into the radio receiver from the drive wire IS. A guide strap 29 is secured to the end of the frame of the condenser 2| and lugs 3| assist in maintaining the coupling 28 on a straight-line path.

As to the signal collector l0 and the junction box II, the former is directly mounted in an insulator member 32 having an elongated neck extending through the mounting bushing 33 of a non-magnetic metal, preferably brass, which in turn is molded into or suitably secured in one end of an insulating shell 34 for the junction box.

The bushing 33 is threaded at its outer end for receiving a nut to mount the junction box and signal collector therewith in any desired position on a mobile craft, on a building, or upon any other structure in which the radio receiver to which the antenna system is to be connected is used. The insulator member 32 also includes a disc-dike portion 36 cut off at one side to provide space for the connection of the signal collector it with an inductance coil 31 by a short lead 38. lhis lead amounts to substantially no more than a junction point. The coil 31 which can be aptly referred to as a booster coil, in one commercial embodiment of the invention is provided in a progressive universal winding which has a relatively low distributed capacity. An annular rim 39 forms a cavity over the greater portion of the inside face of the insulator member 32 for receiving one end of the coil form 4| of insulating material in a snug fit. The opposite end of the coil form 4| is snugly mounted in a cavity formed by-an annular rim 42 on an inner support 43 likewise provided in insulating material. The inner support 43 is cylindrical-like in form and hollow over the inside at 44 to permit movement therein of a slug or core 46 of comminuted iron particles, which passes through an aperture 41 in the inner support for slidable movement over the length of theinduotance coil 3! within the coil form 41. This provides permeability tuning for the antenna circuit. It is essential to have the iron slug 48 as homogeneous as possible, so that there will be no irregularities in the variations in inductance values of the coil as the slug is moved through the same.

At the lower end of the junction box II as it is illustrated in Fig. 2, I provide a combination cap and bushing 48 which is likewise provided in a non-magnetic and non-corrosive material such as brass having an internal cavity for fitting over the end of the insulating shell 34 with a metal grounding washer 43 at the end of the shell and resting upon a shoulder in the cavity of the cap 48. A lead-in separator or insulator member 5| rests upon the washer 49 and includes and apertured spacing portion for receiving the drive wire I6 for the iron slug 4!. The member II also includes a semi-disc-like portion open at one side for receiving the lead-in wire 52 and rigidly spacing the same from the drive wire It so that there is no possibility of short circuiting between the two. A spacing washer 53. of insulating material rests on the top ofpthe lead-in separator 5|, fits snugly within the cavity 64 in the inner support, and limits the outward movement of the iron slug 46 which is illustrated in Fig. 2 in its outermost position.

In order to take up backlash which might occur in the drive wire i5 system, the coiled spring 53 is positioned intermediate the end of the iron slug 46 and the top face of the spacing washer 53. The spring is provided in such a configuration and such a length that it will expand and follow the movement of the iron slug 48 into the inductance coil 31. A coupling 5&3 intermediate the drive wire l5 and iron slugs 4b is illustrated in insulating material. Although an insulator is preferred, it has been found that a conductive coupling for the drive wire and an iron slug can be employed without seriously aifecting the operating characteristics of the coil;

The inductance coil 3'. is connected to the lead-in wire 52 by means or a short lead 51 extending along a channel on the outside surface 01' the inner support it and passes to the inside of such support below the insulating spacing washer 53. A suitable metal shield 58 is provided around the wire 52 on the outside of an insulating sheath 52, and such shield is grounded through the cap and bushing member 48 by soldering the same to the grounding washer to. Afiexi'ole metal housing Si in the flexible shaft 13 for the drive wire i 5 is likewise grounded through the washer ii by being frictionally secured in a neck portion 52 for such washer.

With the above described construction for the junction box, a rugged, simple assembly is provided which will hold together with all types of treatment and positively insulate the coil circuit from the slug and drive wire. Furthermore, the junction box l i is normally mounted in a vertical position either at the bushing 33 or the bushing id. With the former mounting, at least, it is normally exposed to the weather. Although it is closed in a substantially seal-tight manner at the top, if water should get in it will drain away from the coil and out of the bottom of the junction box.

The electrical circuit for the embodiment oi Figs. 1 and 2 is illustrated in Fig. 3 together with diagrammatic representations of some of the mechanical elements thereof. With the coil 31 in substantially direct connection with the aerial i and substantially no impedance there between, and the shielded lead-in l2 interposed between the coil and receiver, the aerial and coil are in a high R. F. voltage held so as to providethe maximum signal energy. The shielded lead-in is in a low E. F. voltage field, and the shield 58 which is effectively a shunt capacitance, provides a low loss in such field. Hence a high gain, low loss antenna circuit is provided. The elements described above are designated by the reference character previously applied to such elements. Those elements of the complete antenna and receiver apparatus which are mounted externally of the radio receiver housing are illustrated on the left-hand side of the line R-R in Fig. 3, while the receiver circuit itself and certain mechanical elements for the antenna system within the housing for such receiver, are illustrated on the right-hand side. of the line R-R. It is understood of course that the cam 23 and drive wire and link mechanism intermediate the cam 28 and the Junction box ll, all on the right side of the line R-R, are included in my complete antenna system. A conventional radio receiver circuit has been illustrated in Fig. 3, and includes a blocking condenser 6 which acts to prevent disturbance of the A. V. C. circuit in the receiver due to leakage on the antenna when wet, for instance. This circuit also includes an antenna input coil cc, and an antenna padder condenser 61 with the latter pro-M viding coupling between the antenna circuit and the portion of the receiver circuit including the coil 66 and tuning condenser 2!. The first R. F. tube 63 is shown in the usual manner for such a member. A decoupling resistor lid is also illustrated in the first R. F. stage, which is completely. shown. The remaining stages are indicated by abbreviated designations. Two decoupling reslstors lid are provided intermediate the second R. F. stage, and the detector, A. V. C., and first audio stage, and an A. V. C. resistor is illustrated at it. The speaker i2 is of course connected with the audio output stage.

As to the operation of the antenna system illustrated in Figs. 1 to 3, when installed with a radio receiver as illustrated in Fig. 3, the radio receiver id is tuned in any of the well-known methods for adjustment of the tuning condenser 25. The position of the cam 23 on the condenser shaft 22 is correlated with the position of the condensers on said shaft and the drive wire it? moves linearly upon rotational movement of the cam 23. The iron slug 46 is moved in and out of the coil 37? upon movement of the drive wire it. In tuning over the broadcast range of frequencies from too is. c. to 1500 k. c. for instance, the slug is positioned substantially out of the coil 8'! at the high frequency end of this range and m telescoped into the coil at the low frequency end. In other words, as illustrated in Fig. 2, the antenna structure is shown in a tuning position at the high-frequency end of the broadcast frequency range. With a variation in inductance for the coil 3?, connected in series with the signal collector ill, the antenna circuit including such signal collector and coil is tuned to correct the frequency of the signal in the antenna circuit to conform to the carrier wave frequency to which the receiver id is tuned. This results in a gain in signal voltage such that the signal energy is materially greater than the signal energy in any of the prior art antenna systems of a comparable size with which I am familiar. This gain is shown-very strikingly in the graph of Fig. '7, which is merely illustrative, and which shows an antenna voltage gain of zero for a ninety-inch metal rod collector which is connected into the receiver circuit directly through an ordinary shielded lead-in, and gains ranging from substantially five to almost fifteen times when employing signal collectors such as shown in Fig. l, which are ten inches to twentyfour inches in length, and connected in series with a variable inductance, and the latter 'connected to a receiver through a shielded lead-in in accordance with my invention. It is understood that these graphs (including Fig. 8) are merely illustrative of the results obtained with" various representative embodiments of my invention, and are not to be considered limiting in any manner. From this graph the possibility of utilizing a very short signal collector member Kill and yet obtain improved radio reproduction is clearly illustrated.

Fig. 3 illustrates graphically the improved signal to noise ratio mentioned in the first part of the specification, which results from the use of my antenna system. Operating a six-tube receiver with 30% modulation and maintaining a one-watt output level, the signal to noise ratio with and without my inductance or booster coil in an antenna circuit including the same signal collector and shielded lead-in, in each instance, is shown. Without the inductance or booster coil in the antenna circuit intermediate the signal collector and shielded lead-in, the percentage of noise with reference to signal increases from 30% noise and 70% signal at the low frequency end of the broadcast spectrum to 50% noise and 50% signal at the higher frequencies. antenna system including the inductance or booster coil, however, and because of the increase in signal energy therefrom, the signal level is raised materially from a comparative standpoint with the noise level. The lower curve shows that the signal to noise ratio varies from 85% signal and 15% noise at the low frequency end, down to 90% signal and 10% noise at the higher frequencies over a range from 600 to 1400 k. 0. Although the curves illustrate the change in ratio rather than the actual signal and noise values, it was found, as has been described above, that the noise level actually decreased while maintaining the same one-watt output because the signal energy is so materially increased'with my antenna system that less amplification is required with less thermal agitation in the tube circuit, and as a result, less noise from this source. The sensitivity curve for the operation with the booster coil in the circuit is also plotted at the top of the illustration, showing improved sensitivity following generally an improved signal to noise ratio. The graph of Fig. 7 showing the representative signal voltage gain curves can also be compared with the signal to noise curve and the former of course shows improved results particularly at the high frequency end.

The modified embodiment of the antenna sys-- tem of my invention is illustrated in Fig. 4. This includes a signal collector or aerial 30'. Such collector is rigidly mounted on insulators l4, and is secured on a car body B at the cowl as illustrated in Fig. 4, although it is understood that it may be similarly mounted in any other desired place. Mounting bolts 16 and i1 extend through the body B, and in this particular illustrated embodiment, the mounting bolts l6 likewise support a bracket 18 grounded to the body B, which bracket supports a junction box or unit 19 similar to the unit ll of Fig, 1. The mounting bolt I6 is insulated from the bracket 18 but is in direct electrical and mechanical connection with the collector III, in fact is effectively a part of the collector. It carries on the inside end, a lug 8| which is in electrical and mechanical connection with such mounting bolt 16, and is adapted to be connected with the inductance coil in the junction box 19 through a short wire 82. The

box or unit 19 is illustrated in greater detail in Using my 2, and the illustration is not repeated in Fig. 5. Instead of providing a mounting bushing at each end of the unit, however, as in Fig. 2, a metal cap 82 is provided having an aperture 86 to permit the extension therethrough of the lead-in cable i2, and the flexible shaft l3. A split static shield 86 for minimizing interference pickup, and with a slit 55 for preventing a short circuiting loop around the inductance coil within the unit, extends over the entire length of the shell 34 and is in electrical and mechanical connection with the bracket 78 at an inturned flange 31 at the mounting end of the unit. This shield may also be applied to the junction box H.

The embodiment of my invention as illustrated in Figs. 1 to 3, is more normally applied as original equipment with a radio receiver. Int/the embodiment of Fig. 4, however, the junction box and flexible shaft assembly can be adapted either asoriginal equipment or as accessory equipment, very readily, to any type of signal collector or aerial, and to the receiver therewith. The drive wire it is connected to a knob or the like 88 which is movable inwardly and outwardly in the usual manner at a mounting bushing 39 which may be secured to the dashboard 9!, in the case of an installation upon an automobile, or to any other convenient structure on an automobile, or any other installation for the receiver In operating this embodiment of my invention, the radio receiver to which the lead-in wire I?! is connected is first tuned to a desired wave frequency. The inductance value for the booster coil in the junction box is varied by adjusting the knob 38 inanually, to in turn move the slug in the coil through the movement of the drive wire, This adjustment can be made while listening to the reproduction from the speaker for the receiver and at the position of the knob when the best reproduction is obtained, the antenna circuit is matched to the receiver circuit. The junction box 19 may of course be used with either slug adjusting apparatus, as also may be the junction box H and collector l0.

A still further modification of myinvention is illustrated in Fig. 6. In many radio installations, as on automobiles, airplanes, and trains, as well as on other more general applications, it is dimcult or undesirable to cut holes through the structure for making a connection to an aerial on the outside. This problem has been satisfactorily solved in the embodiment illustrated in Fig. 6, which includes a signal collector l0" comprising a relatively short rod or wire mounted in a suction cup 93 of insulating material such as rubber or the like. The cup is cemented in a suitable manner upon the outside surface of a windshield 94, for example. The windshield constitutes a very good dielectric, but other panels or the like composed of dielectric material could be used. Before cementing the cup 93 onto the windshield, a. plate 96 of foil or other suitable material is cemented onto the outside surface of the windshield at the position at which the cup 93 is to be secured. The electrical connection from the signal collector l2" to the plate 96,

plished by a spring 91 strong enough to maintain a good electrical contact with the plate 96 but not so strong that any rubbing which hight occur from the spring on the plate 96 would be sufllcient to tear through or injure such plate. A plate 98 similar to the plate 96 is cemented to which acts as one plate of a condenser, is accom- Y the inside of the windshield opposite the plate 96 to provide a complete capacitive coupling intermediate the selector II" and a junction box unit 18 identical with that illustrated in Figs. 4 and 5. A short wire 82 connects the plate 98 of the condenser with the inductance coil in the unit 19. The junction box unit II is rigidly mounted on the cowl B or other suitable portion of the body of the vehicle, and the drive wire I6 for moving the slug in the inductance coil therein can be connected to an adiusting knob as 88 in Fig. 4, or to the cam structure illustrated in Fig. 1. Inasmuch as the glass windshield 84 is a good dielectric and there are relatively no losses through the same and the distance between the end of the selector wires Ill" and the inductance coil in the junction box 19 is extremely short so far as efllciency is concerned, the inductance coil in the box can be considered as being connected substantially directly to the signal collector as in the embodiments illustrated in Figs. 1 and 4. There is impedance introduced into the circuit by use of the capacity connection that is not in the circuit of Fig. 3, for instance, or in the circuit for the modification of Fig. 4. However, where an installation could not be made by cutting through a panel or the like, this embodiment provides a readily adaptable, inexpensive, and efficient structure.

In my invention, as described above, therefore, I provide an antenna system for a radio receiver in which the signal voltage is increased so materially that a relatively short aerial or signal collector can be employed, and still provide a voltage gain over the prior art antenna systems. As a. result of the increased signal voltage output from my antenna, radio receivers for use therewith in installations where the size of the aerial is definitely limited can be made with less sensitivlty than receivers for such installations in the prior art. Less amplification is required in the receiver for the same power output, thus reducing the noise level in the receiver circuit, and in such a case, and even where the amplification remains relatively high, the signal to noise ratio is higher or more favorable because of the increase of the signal voltage in my antenna system. Furthermore, my antenna system can he readily adapted to a radio as original equipment or installed for connection with a radio receiver of any design or type as accessory equipment.

Although I have described my invention in its eierred embodiments, it is understood that the vention is not limited thereto and that changes d modifications may be made therein all withl. the scope of the present invention, and limited only the scope of the appended claims.

I claim:

1. An antenna system for radio apparatus compromising an aerial, a shielded conductor for connection with radio apparatus, a variable inductance coil connected intermediate said aerial and said shielded conductor in series connection with each, and means for varying the inductance in said coil including a metal core for said inductance coil, and means for adjustably moving said core with reference to said coil.

2. An antenna system for radio apparatus comprising an aerial, a shielded conductor for connection with radio apparatus, a variable inductance coil connected intermediate said aerial and said shielded conductor in series connection with each, and means for varying the inductance of said coil, said means including a metal core movable therein, a moving member for operative connection with the radio apparatus and mo able upon tuning of such radio apparatus, said member having a substantially cam-shaped slot therein, and means carried in said slot and operatively connected with said core for moving said core in accordance with the movement of said member.

3. An antenna system for radio apparatus comprising an aerial, a shielded conductor for connection with radio apparatus, a variable inductance coil connected intermediate said aerial and said shielded conductor in series connection with each, and inductance varying means including a metal core movable within said inductance coil, driving means operatively connected with said core, and a manually operated knob connected with said driving means and mounted for adjustable movement to move said core relative to said coil to vary the inductance thereof and tune the antenna system to match the tuning of the radio apparatus to which the antenna system is connected.

4. An antenna system for radio apparatus comprising an aerial, a coil unit adjacent said aerial including a housing, an inductance coil in said housing in electrical connection at one end with said aerial, and a metal core movable over the length of said coil to vary the inductance thereof, means extending out of said housing and connected with said core for accomplishing linear movement of. said core with relation to said coil, and a shielded conductor connected with said inductance coil at the other end thereof for connection to radio apparatus.

5. An antenna system for radio apparatus comprising an aerial, a shielded conductor for connection with radio apparatus, a coil form and a variable inductance coil thereon connected intermediate said aerial and said shielded conductor in series connection with each, and a housing unit for said variable inductance coil including a hollow shell, a pair of insulating supporting members within said shell and with one or" said members at each end of the coil form acting togather to support said coil form at opposite ends thereof, a metal slug movable into and out of said coil form at one end thereof for varying the inductance of said coil, with the supporting memher at such one end of said coil form being hollow to permit the movement of said slug therein, a driving member connected with said slug, insulating means at one end of said hollow supporting member acting with said hollow supporting memher to separate the connection between said coil and said shielded conductor from the driving member for said slug, means at each end of said hollow shell for substantially closing the ends thereof, with at least one of said closing means comprising a mounting bushing for mounting said housing unit, and means operatively connected with said driving member for adjustable movement thereof.

8.1m antenna unit for connection to radio apparatus including a hollow shell of insulating material, an inductance coil fixedly secured in said shell, with one end of, said coil adapted for connection in series with a signal collector, a shielded conductor connected to the other end of said coil, and extending out of said shell, 8. metal core movable through said coil to vary the inductance thereof, means within said shell for insulating such core from said conductor, and a static shield on the outside of said shell for preventing undesirable interference from afiecting said coil having a split portion longitudinally thereof.

7. An antenna unit for connection to radio apparatus including a hollow housing having an opening at each end thereof, an insulator member at one end of said housing and supported therein, a rod-like signal collector rigidly mounted in said insulator member and extending out of said housing, an inductance coil fixedly supported within the housing at one end thereof having one end thereof in series connection with said signal collector, a shielded conductor in series connection with the other end of said inductance coil with said conductor extending out of said housing and adapted for connection to radio apparatus, means for varying the inductance of. such coil within said housing, and mounting means for said unit on at least one end thereof at a housing opening.

8. An antenna system for radio apparatus for installation upon a mobile craft comprising a rod-like aerial, a shielded lead-in for connection with such a radio receiver, and a junction box unit intermediate said aerial and said shielded lead-in, including a hollow shell, a variable inductance coil supported within said shell substantially against movement relative to said shell and connected at one end to said aerial and connected at the other end to said shielded lead-in, and means at one end or the other of said shell for rigidly mounting the same.

9. An antenna system for mounting at a panel of dielectric material comprising a rod-like aerial, means at one end of said aerial for mounting the same on one side of said dielectric panel, a metal plate secured to said dielectric panel beneath said mounting means and on the same side of the dielectric panel, conducting means intermediate said aerial and said plate, a second metal plate secured to said dielectric panel on the other side thereof and in a position corresponding to said first plate, an inductance coil mounted adjacent said second plate and connected thereto at one end of the coil, and a conductor connected to the other end of. said coil for connection to radio apparatus.

10. Radio antenna apparatus including an insulating shell, a coil form fixedly supported within said shell having an inductance coil thereon, insulating means for supporting said form in said shell, an insulatingly supported signal collector for said apparatus connected to one end of said coil, and with said insulating means having an elongated cavity therein adjacent such other end of said form, a metal core slidable in said cavity for movement in and out of said coil form to vary the inductance of said coil, radio receiver connecting means electrically connected to the other end of said coil, and. insulatingly maintained out of contact with the slidable core, and mounting means for said apparatus operatively connected with said insulating shell for rigidly mounting said apparatus.

11. An antenna system for a radio receiver on a mobile craft having a relatively small space for accommodating an aerial for such system, such antenna system comprising in combination an aerial, a shielded lead-in for connection to the radio receiver, a variable inductance coil unit mounted adjacent said aerial and in electrical series connection with said aerial and with said shielded lead-in and connected intermediate the same to increase in the antenna system the signal energy picked up by said aerial and delivered to the radio receiver over the shielded lead-in, and with said variable inductance coil unit being in such an adjacent connected position relative to said aerial to substantially eliminate impedance intermediate said aerial and coil unit, and

means for mounting said variable inductance coil unit in such adjacent position.

12. In an antenna system for a radio receiver having resonant frequency changing means including a rotary shaft, the combination of an aerial, a variable inductance coil unit having a coil in electrical connection with said aerial and in a position adjacent thereto with the connection between the aerial and said coil being such as to substantially eliminate impedance intermediate the same, a variable element for said inductance coil unit being movable with respect to the coil to vary the inductance of the unit, and movable means operatively connected with said variable element to mechanically connect said element with the rotary shaft of the radio receiver including a rotary member operatively connected with said rotary shaft having a cam slot therein, and coupling means having a projection riding in thecam slot to move said variable element upon tuning of the resonant frequency changing means and the corresponding movement of the rotary shaft.

13. A radio receiver antenna system for mounting where lack of space permits only an aerial materially shorter than the length necessary for efficient radio wave reception, including in combination an aerial which is so short as to normally be ineflicient, a variable inductance in electrical connection with said aerial, and conductor means in electrical connection with said variable inductance for connection between the variable inductance and the radio receiver, with said conductor means having capacitance per unit length which is relatively high compared to the capacitance per unit length of the aerial.

14. In a radio receiver antenna system for installation where the available space necessitates an aerial materially shorter than a length necessary to receive radio waves efficiently, the combination of an aerial which is so much shorter than the length of the received radio waves as to normally be inefficient, a variable inductance in substantially direct electrical series connection with said aerial at one end of the inductance and acting to efllciently increase in the antenna system the signal voltage of the radio waves received by the aerial, housing means for said inductance, a conductor in electrical series and substantially direct connection with the other end of the inductance for extending to a radio receiver to transmit the signal energy of the received radio waves thereto, and means connected to ground for shielding said conductor against the pick-up thereon of extraneous noises.

15. In a radio antenna device for mounting on the body of a mobile cra'ft having radio apparatus, thereon with frequency changing means for the apparatus, the combination of insulating means, a signal collector supported by said insulating means, an inductance unit in said insulating means including a coil and a movable core, means operatively connected with said insulating means for mounting said antenna device on the body of said craft, with one end of said coil in electrical connection with said signal collector, and with the other end of said coil adapted to be connected to the radio apparatus, and mechanical means operatively connected with said core and adapted to be connected with the frequency changing means of the radio apparatus to move the core to vary the inductance of the coil upon adjustment of the frequency changing means.

GUS L. MYDLIL. 

